Simultaneous source techniques involve multiple sources (e.g., vibrators) or groups of sources emitting sweeps simultaneously. The resulting seismic record is then separated to obtain records that contain the contribution from only a single vibrator.
Methods for record separation include, for example, simultaneous sweep methods that use a phase rotation scheme for the different sweeps, High Fidelity Vibratory Seismic (HFVS) techniques, and pseudorandom sequence-based sweeps that enhance record separation by minimizing sweep crosscorrelation in an area of interest.
One pseudorandom sequence-based method involves generating a series of codes that are iteratively altered to reduce the sweep crosscorrelation for the time of interest in the correlated record (e.g., from t=0 to between t=2 and t=10 seconds). A second pseudorandom sequence-based method involves using an evolutionary technique (e.g., simulated annealing or genetic algorithm) to generate sweeps that have their crosscorrelation minimized at certain lag-times.
These record separation techniques are effective but must be balanced with the need to efficiently gather seismic data. Efficient survey methods may involve vibrators operating independently of one another with their sweeps occurring at random intervals. Such methods increase survey productivity (other methods require vibrators to wait for other vibrators to finish sweeping before they begin sweeping) but may preclude use of the aforementioned record separation techniques (which may require high amounts of organization between the different sources).